<template>
	<ul class="list">
		<li class="item" v-for="item of letters" :key="item" :ref="item" @click="handleLetterClick"
			@touchstart="handleTouchStart" @touchmove.prevent="handleTouchMove" @touchend="handleTouchEnd"
		>
			{{item}}
		</li>
	</ul>
</template>

<script>
	export default {
		name: 'CityAlphabet',
		props: {
			cities: Object
		},
		computed:{
			letters(){
				const letters=[];
				for(let i in this.cities){
					letters.push(i)
				}
				return letters
			}
		},
		data(){
			return{
				touchStatus: false,
				startY: 0,
				timer: null
			}
		},
		updated() {
			this.startY = this.$refs['A'][0].offsetTop
		},
		methods: {
			handleLetterClick(e) {
				this.$emit('change', e.target.innerText)
			},
			handleTouchStart(){
				this.touchStatus = true
			},
			handleTouchMove(e){
				if(this.touchStatus){
					if(this.timer){
						clearTimeout(this.timer)
					}
					this.timer = setTimeout(()=>{
						const touchY = e.touches[0].clientY - 79
						const index = Math.floor((touchY - this.startY) / 20)
						if(index>=0 && index<this.letters.length){
							this.$emit('change',this.letters[index])
						}
					},16)
				}
			},
			handleTouchEnd(){
				this.touchStatus = false
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list 
		display:flex 
		flex-direction:column 
		justify-content:center 
		position:absolute 
		right:0 
		top:1.58rem 
		bottom:0 
		width:.4rem 
		.item 
			text-align:center 
			line-height:.4rem 
			color:$bgColor
</style>
